Castle Sween is located on the eastern shore of Loch Sween, in Knapdale,[1] south of the forestry village of Achnamara on the west coast of Argyll, Scotland. Castle Sween is thought to be one of the earliest stone castles built in Scotland, having been built sometime in the late twelfth century.[1] The castle's towers were later additions to wooden structures which have now since vanished.[1]

Castle Sween takes its name from Suibhne, whose name was Anglicised as "Sween". He was thought to have built the castle. Suibhne was thought to have been a grandson of Hugh the Splendid O'Neill who died in 1047.[2]